The present disclosure relates to a power amplification circuit.
A power amplification circuit is used in a mobile communication device such as a cellular phone in order to amplify the power of a radio frequency (RF) signal to be transmitted to a base station. When a plurality of amplifiers is used together in a power amplification circuit for example, a switch is employed to control switching on and off of the amplifiers in order to reduce current consumption. For example, Japanese Unexamined Patent Application Publication No. 2000-278109 discloses a high-frequency switch that is formed of two cascode-connected bipolar transistors.
In the high-frequency switch disclosed in Japanese Unexamined Patent Application Publication No. 2000-278109, an input signal is supplied to the base of a first-stage bipolar transistor and an output signal is output from the collector of a second-stage bipolar transistor in accordance with a control signal supplied to the base of the second-stage bipolar transistor. However, since the two bipolar transistors of the switch are cascode connected with each other, the amplitude of the output signal is restricted by the saturation voltages of these transistors. Therefore, the amplitude of the output signal is restricted and the output signal is likely to be distorted when a large signal is input. Consequently, it is difficult to achieve desired linearity characteristics and the operational range in which the switch can be used is narrow. Furthermore, since the bipolar transistor of the second stage needs to be of such a size as to be able to supply a current of the same size as the current supplied to the bipolar transistor of the first stage, an increase in circuit area is incurred due to an increase in the number of elements.